End mills of the type referred to in this application have been the subject of continuous improvement during the last several decades.
Due to a competitive world-wide market, there is ever increasing demand for machining with end mills to provide higher finish and extended tool life, even when machining workpieces at high speeds and/or workpieces made of difficult to machine materials.
Accordingly, even a design modification which provides a size reduction of a discontinuity measurable in microns is considered a significant improvement in performance.
The present application is directed to end mill corners with convex radial relief surfaces and corner radius surfaces (which are flat or concave) connected thereto. To elaborate, an end mill can have, immediately adjacent to a cutting edge thereof, either a flat or concave radial relief surface or a convex radial relief surface. For the purposes of the specification and claims, a convex radial relief surface is defined as a radial relief surface having at least a portion thereof, immediately adjacent to a cutting edge, which is convexly-curved. It will be understood that a radial relief surface that comprises a convex portion immediately adjacent to a cutting edge and then a flat portion (i.e. a portion which, in a plane perpendicular to a rotation axis, follows a straight line) separated from the cutting edge by the convex portion, is also considered a convex radial relief surface. Aligning a flat or concave radial relief surface with a corner radius surface (which is flat or concave) without a surface mismatch is considered less problematic than aligning a convex radial relief surface with such corner radius surface. Therefore the subject matter of the present application refers only to end mills of the type having convex radial relief surfaces.
The present application is also specifically directed to end mills with corners having circular arc profiles. A corner's circular arc profile is presented during rotation of such end mills about a rotation axis and viewed in a direction perpendicular to the rotation axis. For the purposes of the specification and claims, this will be called a “profile view”.
The circular arc profile defines a portion of an imaginary circle. The circle has a circle center point, axial and radial tangent lines, axial and radial tangent points, and a radius magnitude measurable from the circle center point to the circular arc profile. The axial tangent point is located at an intersection of the circle and the axial tangent line which extends forwardly from the circle center point and in a direction parallel with a rotation axis of the end mill. The radial tangent point is located at an intersection of the circle and the radial tangent line which extends radially outward from the circle center point and in a direction perpendicular with the rotation axis.
To describe further features of the end mills in this application, planes may also be defined from the circle. Specifically, a radial tangent plane extends perpendicular to the rotation axis, and both the circle center point and radial tangent point both lie in the radial tangent plane. The radial tangent line also lies in the radial tangent plane. Similarly, other radial lines described hereinafter can be understood to lie in corresponding radial planes extending perpendicular to the rotation axis.
It will be understood that the circle and associated lines, planes, tangent points and radius magnitude, are imaginary and hence are not visible features on an end mill but rather are derivable through the construction thereof.